Screening And Identification Of Lactic Acid Bacteria Producing Active Substances Inhibiting Toxoplasma Gondii

Toxoplasma gondii is an important food-borne zoonotic parasite.Widely infects people and other warm-blooded animals.Food is easily contaminated with Toxoplasma during processing,increasing the risk of infection and threatening human health.The aim of this study was to screen lactic acid bacteria producing toxoplasmo-inhibiting active substances,and to verify the insecticidal active substances,as well as strain identification and gene analysis.In this study,a method was developed to determine the killing of toxoplasma tachyzoites in lactic acid bacteria supernatant.On this basis,the supernatant of310 strains was treated to remove organic acid and hydrogen peroxide,and 18 strains were screened out with insecticidal effect of more than 50%.Among them,Lactiplantibacillus plantarum YXAR-8 and XAR-1 had the best insecticidal effect,and the ratio of PI-positive tachyzoites were 91.56% and 88.30%,respectively.The results showed that the supernatant of strains YXAR-8 and XAR-1 had the best killing effect on tachyzoites of T.gondii when the incubation time was 60 min,and the ratio of PI-positive tachyzoites were 91.85% and90.18%,respectively.Protease hydrolysis of the target strain showed that protease E,protease K and trypsin all reduced the ratio of PI-positive tachyzoites in the target strain.Among them,adding protease K into the supernatant of strain YXAR-8 had the best killing effect on the tachyzoites of T.gondii,and the ratio of PI-positive tachyzoites decreased by69.03% compared with the control group(22.58%).When trypsin was added into the supernatant of strain XAR-1 showed the best killing effect on T.gondii tachyzoites,and the ratio of PI-positive tachyzoites decreased by 78.99% compared with the control group(10.21%).The insecticidal active substances in the supernatant were mainly protein substances.Physiological,biochemical and 16 S r DNA identification showed that the two strains were Lactiplantibacillus plantarum.The genes related to drug resistance were found in the whole genome of the two strains,indicating that the two strains have certain safety.This study provides a basis for expanding the application of lactic acid bacteria in food industry and a new idea for reducing the food safety risks caused by parasites in food processing.